Orthogonal frequency-division multiplexing (OFDM) is a modulation technique used at the physical layer (PHY) of a number of wireless networks, e.g., networks designed according to the IEEE 802.11a/g, and IEEE 802.16/16e standards. OFDMA is a multiple access scheme based on OFDM. In OFDMA, separate sets of orthogonal tones (subchannels) and time slots are allocated to multiple transceivers (users) so that the transceivers can communicate concurrently. As an example, the IEEE 802.16/16e standard has adopted OFDMA as the multiple channel access mechanism for non-line-of-sight (NLOS) communications at frequencies below 11 GHz.
In a conventional OFDMA-based cellular network, e.g., a wireless network according to the IEEE 802.16/16e standard, incorporated herein by reference. The network confines operations to a point-to-multipoint topology, wherein only two types of network entity exist, namely base stations (BS), and mobile stations (MS). The BS manages and coordinates all communications with the MS in a particular cell. Each MS is in direct communication with only the BS, and only the BS communicates with an infrastructure or “backbone” of the network. That is, there is only one hop between the MS and the BS. All communications between the MS must pass through the BS. Furthermore, there is one connection between the BS and each MS.
Due to significant loss of signal strength along the connection for certain spectrum, the coverage area of wireless service is often of limited geographical size. In addition, blocking and random fading frequently results in areas of poor reception, or even dead spots. Conventionally, this problem has been addressed by deploying BSs in a denser manner. However, the high cost of BSs and potential increase in interference, among others, render this approach less desirable.
In an alternative approach, a relay-based network can be used. This network includes multiple mobile stations (MS) and/or subscriber stations (SS). A relatively low-cost relay station RS extends the range of the BS. Some of the stations can communicate directly with the BS. Other stations can communicate directly with the RS and indirectly with the BS. Obviously, communications on the link between the RS and BS or between two adjacent RSs (i.e., relay link) can become a bottleneck.
It is recognized that new functions need to be provided for protocols operating on links in mobile multihop relay (MMR) networks. For example, traffic forwarding and routing now becomes essential at a relay station (RS) because multiple hops can exist between the source and destination of the traffic. Moreover, new quality of service (QoS) and security challenges have to be addressed properly in the MMR network.
Unfortunately, the legacy format of the media access (MAC) protocol data unit (PDU) specified by the IEEE 802.16e standard is highly restrictive and rigid, and cannot be used without any extension or modification to support such a wide variety of needs particular for networks designed according to the IEEE 802.16j standard.
As a result, a proper format is needed for MAC PDU on relay link.